Pro: The Best Induction for the Physiologically Difficult Airway is Ketamine-Propofol Admixture (“Ketofol”)

Abstract

THE INDUCTION AND INTUBATION of critically ill patients are high-risk interventions, with nearly half of patients experiencing a major adverse event, such as cardiovascular instability, severe hypoxia, or cardiac arrest. 1 Russotto V Myatra SN Laffey JG et al. Intubation practices and adverse peri-intubation events in critically ill patients from 29 countries. JAMA. 2021; 325: 1164-1172 Crossref PubMed Scopus (98) Google Scholar Preexisting physiologic derangements are a major contributor to decompensation, and the term “physiologically difficult airway” is used to describe patients with significant physiologic alterations prior to airway management. 2 Myatra SN Divatia JV Brewster DJ. The physiologically difficult airway: An emerging concept. Curr Opin Anaesthesiol. 2022; 35: 115-121 Crossref PubMed Scopus (6) Google Scholar Although many factors may contribute to a patient with a physiologically difficult airway, the derangements of most concern are hypotension, hypoxia, severe metabolic acidosis, and right ventricular dysfunction. 2 Myatra SN Divatia JV Brewster DJ. The physiologically difficult airway: An emerging concept. Curr Opin Anaesthesiol. 2022; 35: 115-121 Crossref PubMed Scopus (6) Google Scholar Inducing a patient who is already hypotensive can be dangerous, as both the induction agents, as well as positive-pressure ventilation, can worsen hypotension. Risk factors for periintubation hypotension have been explored recently, and one study derived and validated a scoring system for periintubation hypotension in critically ill patients (C-statistic 0.75 [95% CI 0.72-0.78]). 3 Smischney NJ Kashyap R Khanna AK et al. Risk factors for and prediction of post-intubation hypotension in critically ill adults: A multicenter prospective cohort study. PLoS One. 2020; 15e0233852 Crossref PubMed Scopus (15) Google Scholar Given the literature surrounding the negative downstream effects of hypotension on the critically ill, one could argue that preventing further decreases in blood pressure is the most important consideration when faced with intubation in a patient with preexisting hypotension. For example, a multicenter cohort study demonstrated that mean arterial pressures ≤65 mmHg in critically ill patients were associated with an increased risk of 30-day major adverse cardiac or cerebrovascular events and increased 30-day mortality. This held true even for hypotension of limited duration. 4 Smischney NJ Shaw AD Stapelfeldt WH et al. Postoperative hypotension in patients discharged to the intensive care unit after non-cardiac surgery is associated with adverse clinical outcomes. Crit Care. 2020; 24: 682 Crossref PubMed Scopus (12) Google Scholar Preexisting hypoxia is also a significant risk factor for decompensation because any apnea time is tolerated poorly by patients with limited arterial oxygen content reserve. Additionally, induction agents typically worsen the ventilation-perfusion mismatch that is already present to some degree in hypoxic patients. Hypoxia, in general, also places patients at greater risk for hemodynamic instability, arrhythmia, and cardiopulmonary arrest. 3 Smischney NJ Kashyap R Khanna AK et al. Risk factors for and prediction of post-intubation hypotension in critically ill adults: A multicenter prospective cohort study. PLoS One. 2020; 15e0233852 Crossref PubMed Scopus (15) Google Scholar Severe metabolic acidosis contributes to a physiologically difficult airway, as any apnea time will result in an increased PaCO2 and a worsening acidosis. Preexisting right ventricular dysfunction presents many challenges to intubation, as the rise in PaCO2 with induction will result in increases in pulmonary arterial pressures and right ventricular strain. Additionally, positive-pressure ventilation tends to overall reduce preload and may precipitate cardiovascular collapse due to insufficient preload to a poorly functioning right ventricle. Patients with a physiologically difficult airway may possess one or a combination of these physiologic derangements. Once a physiologically difficult airway is identified, the next challenge for the clinician is to design an induction regimen that would be best tolerated by a patient with preexisting physiologic challenges.